Couplings, such as sleeves and unions, are widely used as fittings for tubes. In a typical joint between two tubes, a sleeve is swaged to a tube and a union is swaged to another tube. The sleeve fits inside the union and is held in the union with a hold-down nut in order to join the tubes. Thus, the integrity of the joint depends in part on the quality of the swaging of the sleeve and union on the respective tubes.
FIG. 1 shows a cross-sectional view of a typical swaged coupling. A coupling 10 has a first end 12 and a second end 14. The first end 12 includes a first coupling groove 16 and a second coupling groove 18. The first and second coupling grooves 16 and 18 typically have a same coupling groove depth. The second end 14 has a substantially constant inner diameter.
The coupling 10 is swaged onto a tube 20 at a first end 22 of the tube. In a typical swaging process, an elastomeric swaging tool (not shown) is used to attach the coupling 10 onto the tube 20. The swaging tool presses and deforms the tube 20 into the first and second grooves 16 and 18 of the coupling 10. First and second swage grooves 24 and 26 of the tube each have a swage groove depth A that is the difference between the inner diameter of the tube 20 measured in the first coupling groove 16 or the second coupling groove 18 and the inner diameter of the tube 20 measured adjacent to the second end 14 of the coupling 10.
The swage groove depth A determines the quality of the attachment of the coupling 10 to the tube 20. If the elastomeric swaging tool operates at an excessive pressure, the swage groove depth A will be too great. This can result in a stress-crack failure of the coupling 10 in the vicinity of the first or second coupling grooves 16 or 18. On the other hand, if the elastomeric swaging tool operates at an insufficient pressure, then the swage groove depth A will be too small. This can result in fluid leaking past the coupling 10 and out of the tube 20. It will be appreciated that, over time, leakage can worsen as the fluid in the tube 20 is heated and cooled and the fluid system is pressurized and depressurized. In applications subject to shock and vibration, such as in aircraft systems, the coupling 10 can separate from the tube 20, causing rapid fluid loss and possible failure of an associated system.
Further, the condition of the elastomeric swaging tool degrades over time. Thus, the elastomeric swaging tool can operate at a pressure other than the pressure set by the operator. Therefore, the quality of the attachment of couplings 10 to tubes 20 can deteriorate over time.
This can result in an increased number of failures. In order to timely detect swage groove depths that may be out of specification, it would be desirable to nondestructively measure the swage groove depth A during the swaging process. Nondestructive evaluation techniques have been used in a number of other industrial applications. For example, nondestructive evaluation techniques using a probe and a transducer have been applied to hole profile gauging systems. See U.S. Pat. No. 5,010,658 ("the '658 patent"). In the '658 patent, a probe senses deviations in the contour of the inner surface of a bore while the probe is retracted through the bore. A profile gauge includes a processing unit that samples the output from the probe, develops a profile for the hole, and evaluates whether the profile is within predetermined tolerance limits. The probe includes a split-ball probe coupled with a transducer, and the probe is retracted through the bore by a spring coupled with a damping device. Because the split-ball probe has only two fingers, centering of the probe cannot be ensured. Thus, accuracy of measurements depends on the skill of the operator. Further, the spring and damping device prevent the operator from receiving tactile feedback information regarding centering of the probe. Measurement gauges have also been adapted for measuring depth of holes for fasteners. See U.S. Pat. Nos. 5,189,808 and 4,112,355.
However, in-process measuring systems known in the prior art have been unable to nondestructively measure swage groove depth. In addition to the shortcomings discussed above, prior art nondestructive measurements are not readily repeatable because a consistent starting point for measurement is not provided. Because these problems have not been overcome by the prior art, the only process verification known in the prior art for the swaging process is via destructive evaluation. Typically, a swaged coupling is cut cross-sectionally and the swage groove depth A is manually measured for an entire lot of swaged couplings. The cross section is typically mounted with plastic, the surfaces are polished, and edge surfaces of the cross section are evaluated with a microscope.
The destructive evaluation process is time consuming, expensive, and statistically inappropriate. For example, if the destructively evaluated sample is within a predetermined specification, then the entire lot is accepted. This can result in the acceptance of swaged couplings in the lot that may have a swage groove depth A outside the predetermined specification. On the other hand, if the swage groove depth A is outside the predetermined specification, then the entire lot is rejected. This can result in the rejection of many couplings in the lot that may have a swage groove depth A within the predetermined specification.
The present invention is directed to providing a semiautomated system and method for swaged coupling process verification that overcome the foregoing and other disadvantages of destructive evaluation as well as in-process measurement devices for other applications. While designed for use in the verification of swaged couplings intended for use in aircraft systems, it is to be understood that the process verification in accordance with the present invention may also find use in other environments, including shipboard applications, military applications, and other industrial applications.